Hopefully this is not a thread hijack, but I was going to post basically the identical question/issue. If this sounds different, then let me know and I'll start a different thread.
In my case, I will narrow it down to a sequence of four 10-minute Ha frames that I took consecutively. When I look at the raw frames, they look pretty much identical except for an occasional satellite or cosmic ray hit. However, after I run them through the image integration process, three out of the four have their signal nearly eliminated. After running the calibration script, images 1, 2, and 4 in the sequence look nearly black (even after STF), while image 3 looks similar to the raw frame. I tried eliminating the flat frame from the integration, but that didn't change anything. I also tried changing the noise evaluation algorithm, but that didn't matter either.
To see it visually, I've captured a screenshot showing two raw frames on the bottom row (image 3 & 4 in the sequence) along with the corresponding calibrated frames above them. STF was applied to all four images.
The four raw frames, four calibrated frames, and master dark/bias/flat can be found here:
https://www.dropbox.com/sh/jeg7g5r14yuvbds/AAB8C5jOvCZn8fBsoZSTCcNAa?dl=0I've attached a csv file from a run with a BatchStatistics script against the four raw frames. The data looks nearly identical between all four images, at least from what I can see.
Below is the console output from the integration process for the four frames. Note the significant differences in k0, s0, and n0 values between image 3 (the good image after calibration) vs. the other three images:
Writing output file: C:/Users/Kathy/Desktop/PI_cache/IC5146/Cal2/IC5146_Ha_600sec_1x1_0C_20170823_0005_c.xisf
Dark scaling factors:
k0 = 0.545
Gaussian noise estimates:
s0 = 5.145e-10, n0 = 0.857 (K-Sigma)
Writing image: w=3326 h=2504 n=1 Gray Float32
70 FITS keyword(s) embedded.
Writing output file: C:/.../IC5146/Cal2/IC5146_Ha_600sec_1x1_0C_20170911_0001_c.xisf
Dark scaling factors:
k0 = 0.550
Gaussian noise estimates:
s0 = 8.517e-09, n0 = 0.821 (K-Sigma)
Writing image: w=3326 h=2504 n=1 Gray Float32
70 FITS keyword(s) embedded.
Writing output file: C:/.../IC5146/Cal2/IC5146_Ha_600sec_1x1_0C_20170911_0003_c.xisf
Dark scaling factors:
k0 = 0.158
Gaussian noise estimates:
s0 = 3.018e-04, n0 = 0.258 (MRS)
Writing image: w=3326 h=2504 n=1 Gray Float32
70 FITS keyword(s) embedded.
Writing output file: C:/.../IC5146/Cal2/IC5146_Ha_600sec_1x1_0C_20170911_0002_c.xisf
Dark scaling factors:
k0 = 0.552
Gaussian noise estimates:
s0 = 2.247e-08, n0 = 0.807 (K-Sigma)
Writing image: w=3326 h=2504 n=1 Gray Float32
70 FITS keyword(s) embedded.
Writing output file: C:/Users/.../IC5146/Cal2/IC5146_Ha_600sec_1x1_0C_20170911_0004_c.xisf
Dark scaling factors:
k0 = 0.559
Gaussian noise estimates:
s0 = 9.518e-09, n0 = 0.820 (K-Sigma)
Writing image: w=3326 h=2504 n=1 Gray Float32
70 FITS keyword(s) embedded.
